1. Field of the Invention
The present invention relates to an organic light emitting display (OLED) device (or organic electroluminescent display device), and more particularly, to an OLED device having an automatic brightness control apparatus that can control the luminance of an image display portion according to the brightness of ambient light.
2. Description of the Related Art
An organic light emitting display (OLED) device is a display device in which electrons and holes are injected into an organic thin layer through a cathode and an anode and recombined to generate excitons, thus emitting light of a certain wavelength. Since the OLED device makes use of self emissive display devices, it requires no additional light source unlike a liquid crystal display (LCD).
Also, the luminance of an organic light emitting diode constituting the OLED device depends on the amount of current flowing through the organic light emitting diode.
The OLED devices may be classified into a passive matrix type and an active matrix type depending on the driving method. The passive matrix OLED device includes anodes and cathodes, which are arranged perpendicular to each other, and is driven by selecting a line. Since the passive matrix OLED device has a simple configuration, it can be realized by a simple process. However, in realizing a large screen, the passive matrix OLED device consumes a large amount of current and cannot drive each light emitting diode for a long time.
On the contrary, the active matrix OLED device controls the amount of current supplied to a light emitting diode using an active device. A thin film transistor (TFT) is typically used as the active device. Although the active matrix OLED device has a comparatively complicated construction, it consumes a small amount of current and can extend an emission time.
A typical OLED device emits light at a range of luminance irrespective of ambient light. Thus, even if the ambient light is dark, the OLED device may emit light at high luminance. The life span of an organic light emitting diode depends on the amount of current flowing through the diode. When the organic light emitting diode emits light at unnecessarily high luminance, the amount of current flowing through the organic light emitting diode increases. As a result, the lifetime of the organic light emitting diode decreases and power consumption increases.
For these reasons, it is desirable to control the luminance of the organic light emitting diode according to ambient light.